1. Field of the Invention
The present invention relates to a simulator for testing an anti-lock braking system (hereinafter simply referred to as "ABS"), and more particularly to a simulator for testing an ABS modulator capable of simulating the yawing during actual road travel and the disproportionate concentration of a vehicle weight, and testing the performance of an ABS modulator with respect to the weight of diverse vehicles.
2. Description of the Prior Art
Currently, in order to prevent the locking of wheels if a braking system is operated while driving a vehicle, an ABS is mounted to the vehicle, which employs a hydraulic braking system. The locking state denotes that, when a driver suddenly steps on a brake while driving, the rolling motion of the wheels is brought to a halt by the braking system mounted to the respective wheels. At this time, if the inertia force of the vehicle is so large as to exceed a frictional force between the tires and road surface, the vehicle continuously slips along the road in the travelling direction of the vehicle. Due to the slip, the frictional force is further decreased to lengthen the braking distance. In addition to this, since the frictional force is greatly decreased, the vehicle is unable to be steered, regardless of manipulation of a handle thereof, thereby possibly bringing about a disastrous accident.
In the hydraulic braking system, generally, hydraulic pressure produced while using a brake pedal is transmitted from a master cylinder to the wheel cylinders of the respective wheels. The wheel cylinder acts to decelerate the wheel speed or stop the operation of the wheel. With this action, the vehicle is decelerated or stopped. The ABS prevents the locking phenomenon to ensure the stability of straight traveling and the steering performance of the vehicle even in a situation of sudden stoppage by means of automatically controlling the braking pressure of the brake so as to completely achieve braking within the shortest possible distance. For these functions, the ABS is provided with a set of speed sensors for monitoring the speed of respective wheels, and automatically increases, decreases and maintains the hydraulic pressure of the braking in accordance with the monitored speed.
The preferable method for testing the performance of the ABS is to actually mount the ABS to a vehicle and allow the vehicle to actually travel along a road with different surface conditions, as, for instance, a dry surface, a wet surface, a frozen surface, etc. Presently, however, various kinds of vehicles are manufactured and diverse options may be added to a single vehicle type with the consequences of high of costs, manpower and time to effect the performance tests of all the ABSs available on the market with respect to every kind of vehicle.
Owing to the above-described reasons, a testing apparatus capable of testing the performance of an ABS within a narrow space has been developed. For example, U.S. Pat. No. 5,101,660 (issued to La Belle) discloses a dynamometer apparatus for testing two and four wheel drive vehicles under simulated road conditions. Here, the apparatus includes a front roll and a rear roll for engaging the front and rear wheels of the vehicle, an electric motor coupled to each roll, a force transducer and a speed sensor coupled to each roll.
Almost all ABS testing apparatuses described as above are constructed to be furnished with a brake test stand, in which, under the state of mounting the ABS to an actually-used vehicle, respective wheels are placed on a pair of front-wheel driving rollers and a pair of rear-wheel driving rollers allotted to the respective front wheels and rear wheels or on pairs of driving rollers allotted to four wheels, and these pairs of driving rollers are driven to operate the ABS for testing the performance thereof. However, such a testing apparatus cannot simulate Various travelling conditions, e.g., the yawing of the wheels and the disproportionate concentration of the vehicle weight, making it impossible to evaluate accurate performance of the ABS. Otherwise, driving motors are supplied to respective pairs of driving rollers for driving the wheels, thereby increasing installation costs. Furthermore, most of the testing apparatuses are incorporated between the driving motor and pairs of driving rollers, with a sliding-control member, e.g., an electronic clutch, for controlling a sliding characteristic between the wheels and driving roller pairs, which also induces the increase of installation costs.